Classic Protocol

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Documentation on the server protocol used by the Minecraft Classic Creative server. Communication


To be able to connect to a server in Minecraft Classic from the Server List, a server must broadcast to a so-called "heartbeat" every few minutes.

The stock server broadcasts this heartbeat every 45 seconds.

A "heartbeat" takes the form of an HTTP request to After sending a heartbeat, the URL for the server is returned.

It can be a GET or POST request. A table of the required parameters is below:

Name Details
port Port number of the server. This is usually 25565
max Maximum number of players on the server
name The name of the server
public Whether the server is public (i.e. appears in the server list) or not. Can be True or False, in that capitalization.
version Protocol version number, this should be 7 unless you're using a client version older than 0.28.
salt A random, 16-character base-62 salt
users Number of users connected to the server

The simplest way to send a heartbeat is to open a TCP socket to port 80 on, and send the following (with the values changed, obviously):

GET /heartbeat.jsp?port=25565&max=32&name=My%20Server&public=True&version=7&salt=wo6kVAHjxoJcInKx&users=0, plus a CRLF(Carriage-return and Line feed).

Make sure any strings, like name, are escaped.

If everything goes well, in the response body you'll receive a URL to the server. Otherwise you'll get a nice HTML error message. There aren't an HTML headers to parse, as the HTTP version is not specified so HTTP/0.9 is used, which does not have headers.

User Authentication

The "key" provided when a user joins the server can be compared to the MD5 checksum of the server's "salt" plus the username to verify that the user is logged in to with that username. This is useful for establishing enough trust of the name provided to ban or op the player by name.

if( player.key == md5( server.salt + ) ) {
 // player is logged in via
} else {
 // player is forging the username

Note: This means that you should make sure your "salt" is kept a secret and shared only with heartbeat.jsp. If your server's "salt" is visible anywhere to users, it is trivial for users to produce valid-looking "key"s without being logged in to


Skins for a player are downloaded by the client from, where skinname is the name of the player. This means that the name for a player can be faked to give a desired skin.

Packet Protocol

The connection is done over TCP. Every packet starts with a byte representing the Packet ID.

Protocol Data Types

Type Size [bytes] Description
Byte 1 Single byte integer (0 to 255)
SByte 1 Single byte signed integer (-128 to 127)
Short 2 Signed integer, network order (-32768 to 32767)
String 64 US-ASCII/ISO646-US encoded string padded with spaces (0x20)
Byte array 1024 Binary data padded with null bytes (0x00)

Client → Server packets

Packet ID Purpose Field Description Field Type Notes
0x00 Player Identification Packet ID Byte Sent by a player joining a server with relevant information. Current protocol version is 0x07.
Protocol version Byte
Username String
Verification key String
Unused Byte (0x00)
0x05 Set Block Packet ID Byte Sent when a user changes a block. The mode field indicates whether a block was created (0x01) or destroyed (0x00).

Block type is always the type player is holding, (even when deleting).

Client assumes that this command packet always succeeds, and so draws the new block immediately. To disallow block creation, server must send back Set Block packet with the old block type.

The XYZ coordinates of the block are just shorts representing the coordinate of the block. (As opposed to player coordinates where the lower 5 bits are fractional coordinates)

X Short
Y Short
Z Short
Mode Byte
Block type Byte
0x08 Position and Orientation Packet ID Byte Sent frequently (even while not moving) by the player with the player's current location and orientation. Player ID is always 255, referring to itself. Player coordinates are fixed-point values with the lowest 5 bits representing the fractional position (i.e. divide by 32 to get actual position in terms of block coordinates). The angle parameters are scaled such that a value of 256 would correspond to 360 degrees.
Player ID Byte
X Short
Y Short
Z Short
Yaw (Heading) Byte
Pitch Byte
0x0d Message Packet ID Byte Contain chat messages sent by player. (See How chat works)
Unused Byte (0xFF)
Message String

Server → Client packets

Packet ID Purpose Field Description Field Type Notes
0x00 Server Identification Packet ID Byte Response to a joining player. The user type indicates whether a player is an op (0x64) or not (0x00) Current protocol version is 0x07.
Protocol version Byte
Server name String
Server MOTD String
User type Byte
0x01 Ping Packet ID Byte Sent to clients periodically. The only way a client can disconnect at the moment is to force it closed, which does not let the server know. The ping packet is used to determine if the connection is still open.
0x02 Level Initialize Packet ID Byte Notifies player of incoming level data.
0x03 Level Data Chunk Packet ID Byte Contains a chunk of gzipped map (not level.dat file). The decompression must be done on the all the chunks sent in Level Data Chunk packets together, not independently. After decompression the map consists of a big-endian int(4 bytes) containing the number of blocks, followed by a raw map array. (chunk is up to 1024 bytes, padded with 0x00s if less).
Chunk Length Short
Chunk Data Byte Array
Percent Complete Byte
0x04 Level Finalize Packet ID Byte Sent after level data is complete and gives map dimensions. The y coordinate is how tall the map is.
X Size Short
Y Size Short
Z Size Short
0x06 Set Block Packet ID Byte Sent to indicate a block change by physics or by players. In the case of a player change, the server will also echo the block change back to the player who initiated it.
X Short
Y Short
Z Short
Block Type Byte
0x07 Spawn Player Packet ID Byte Sent to indicate where a new player is spawning in the world. Position and orientation are encoded the same as for packet 0x08 below. PlayerID -1 (255 unsigned) indicates the player's self. This will set the player's spawn point.
Player ID SByte
Player Name String
X Short
Y Short
Z Short
Yaw (Heading) Byte
Pitch Byte
0x08 Position and Orientation (Player Teleport) Packet ID Byte Sent with changes in player position and rotation. Teleports player it's sent to if player ID < 0 (For sending initial position in map, and /tp)
Player ID SByte
X Short
Y Short
Z Short
Yaw (Heading) Byte
Pitch Byte
0x09 Position and Orientation Update Packet ID Byte Sent with changes in player position and rotation. Sent when both position and orientation is changed at the same time.

Not required for server operation.

Player ID SByte
Change in X SByte
Change in Y SByte
Change in Z SByte
Yaw (Heading) Byte
Pitch Byte
0x0a Position Update Packet ID Byte Sent with changes in player position.

Not required for server operation.

Player ID SByte
Change in X SByte
Change in Y SByte
Change in Z SByte
0x0b Orientation Update Packet ID Byte Sent with changes in player rotation.

Not required for server operation.

Player ID SByte
Yaw (Heading) Byte
Pitch Byte
0x0c Despawn Player Packet ID Byte Sent when player disconnects.
Player ID SByte
0x0d Message Packet ID Byte Messages sent by chat or from the console. (See How chat works)
Player ID SByte
Message String
0x0e Disconnect player Packet ID Byte Sent to a player when they're disconnected from the server.
  1. "Cheat detected: Distance" - happens not only when setting tile too far away from the player (how far is maximum distance and how it is measured?), but also when player moves and then immediately builds.
  2. "Cheat detected: Tile type"
  3. "Cheat detected: Too much clicking!"
  4. "Cheat detected: Too much lag"
Disconnect reason String
0x0f Update user type Packet ID Byte Sent when a player is opped/deopped. User type is 0x64 for op, 0x00 for normal user.
User type Byte

Player Position

Fixed Point

Player position is represented via X, Y, and Z fixed-point coordinates. The fractional portion is 5 bits, so dividing the short integers received in position update packets by 32, you will have floating point coordinates for the player. This position corresponds to the center of the client viewport.

Standing On Things

The bottom of the player's feet is located 1.59375 (fixed-point: 51) units below the center of the viewport, so to position the player on top of a particular block you could send a teleport (0x08) packet specifying a Y value based on the block position as: (Y x 32 + 51)


A yaw value of 0 means the player is facing in the Z=0 (negative Z) direction. This value increases in a clockwise direction as seen from above. If we call the negative Z direction "North", then a yaw of 64 means "East", 128 means "South", and 192 means "West".

A pitch value of 0 means level and this value increases in a downward direction. 64 is down, and 192 is up. Values of 65 to 191 should never occur because the player cannot look further up or down than the 64 → 0, 255 → 192 range. However, the Minecraft Classic client does not ignore invalid values, so it is possible to make players' heads "upside-down".

Color Codes

Messages sent from the server to the client can contain color codes, which allow coloring of text for various purposes.

An ampersand followed by a hex digit in the message tells the client to switch colors while displaying text.

Colour coding at the start of the message will only work if the player ID byte is less than 127. If it's 127 or higher, the game automatically adds &e before the message, making it yellow. However, colour codes after the first character still work. If you use an ID below 127, it doesn't add a colour code, so the ones you use will work.

It is important to note that an ampersand at the end of a message that is not followed by a hex digit will crash all clients that receive it, so it is a must to sanitize chat messages received from clients.

Hex digit to color mapping
Sample Code Common Name Foreground Color Background Color
&0 Black 0 0 0 0 0 0
&1 Dark Blue 0 0 191 0 0 47
&2 Dark Green 0 191 0 0 47 0
&3 Dark Teal 0 191 191 0 47 47
&4 Dark Red 191 0 0 47 0 0
&5 Purple 191 0 191 47 0 47
&6 Gold 191 191 0 47 47 0
&7 Gray 191 191 191 47 47 47
&8 Dark Gray 64 64 64 16 16 16
&9 Blue 64 64 255 16 16 63
&a Bright Green 64 255 64 16 63 16
&b Teal 64 255 255 16 63 63
&c Red 255 64 64 63 16 16
&d Pink 255 64 255 63 16 63
&e Yellow 255 255 64 63 63 16
&f White 255 255 255 63 63 63